Motion control is a common fundamental technology for all machine controllers to control the speed, position and torque of a motor used on various machines for driving cutting tools or chucks in the 3-D space to perform cutting, manufacturing, assembly, fetching and other automated motions along an expected trajectory with expected speed at expected time. There are two types of conventional motion control servo loop: open-loop control, and closed loop control using proportional-integral-derivative (PID) control.
Open-loop control is performed by a pulse generator outputting position commands inside a controller without a feedback signal for comparison and error calculation. Therefore, it fails to improve system performance such as the response speed and the steady-state error, and is only suitable for low-end control.
On the other hand, the proportional-integral-derivative (PID) control loop matches with the feed-forward controller to provide proportional, integral and derivative calculations. The proportional controller is a constant gain controller using a feedback signal to correct errors and enhance the response speed. The derivative controller is capable of differentiating the error with respect to time so as to improve the transient response. The integral controller is capable of integrating the error so as to eliminate the steady-state error as the system reaches the steady state. However, even though the integral control loop is capable of eliminating the steady-state error, the response speed is lowered. Therefore, it fails to respond to the change in the system in real-time. If the parameters such as the integral gain and the integral time are set too large, the controlled system will be unstable due to oscillation caused by rapidly increased accumulated error. The servo significantly lags under high speed control, which causes slow response, affects the tracking accuracy and is not useful in high precision control.
Accordingly, in order to meet the requirement of high speed and high precision of a high-end motion controller, the currently available motion control servo loop has to be improved so as to enhance the control performance and overcome the aforesaid problems regarding accuracy and stability.